You should adjust the chain to spec in the tightest spot.
If the tight spots can't be worked out with lube and some excercise, a new chain is in your near future.
The standard story is to replace the chain and sprockets together. You can get away with just a chain replacement if your sprockets don't show any signs of wear when compared to what a new one looks like. Since you have a broken tooth, the sprocket should be changed with the chain. Since you're doing that, you should replace the front one, too, no matter what it looks like. You can't go wrong that way.
To check the front one, just remove the allen bolts from the cover.
CAUTION: While the cover is loose or off be sure no one moves the clutch lever or you may end up with a mess and a need to rebuild the clutch slave cylinder.